Various types of push-pull free-running inverters have been extensively used for converting one d-c voltage to another in power supply applications. Some utilize transistor circuitry for control of the various parameters including output voltage, current and frequency of the inverter.
One simple and reliable type of free-running inverter utilizes transformer feedback with frequency control being maintained by a saturable transformer in the feedback circuit. Several basic circuits of this type are disclosed in an article by James Lee Jensen entitled: "An Improved Square-wave Oscillator Circuit" IRE Transactions on Circuit Theory, Sept. 1957, pp 276-279. Where a number of such inverters are being utilized together, it is desirable that they be synchronized together in order to eliminate any low frequency beating effects. In applications where such a circuit is being used to power digital circuitry, it may be desirable to synchronize the inverter to a factoral frequency of the digital system clock. Any switching spikes produced by the inverter are then likely to occur when the digital system is changing states thus making it less susceptible to transient noise.
Synchronization control of such a basic circuit may be achieved in a number of ways such as by inducing a voltage spike across the primary of the saturable transformer to induce earlier saturation. However such an arrangement requires a change in the feedback circuitry parameters thereby adding another feedback control circuit with its attendant problems.